Evolution of competitiveness during wheat domestication

Crop domestication involved adaptation of wild plants to human exploitation,1,2,3,4 but the underlying selection mechanisms remain unclear.2,4 Archaeological evidence from the best-studied regions shows domestication occurring across a diffuse region and protracted period of at least 1,000-2,000 years,2,5,6,7 consistent with a co-evolutionary process.2,3 For seed enlargement, both theory2,6,8,9,10 and empirical evidence11,12,13 indicate an unintentional evolutionary mechanism, potentially acting via an ecological process such as competition,14,15,16 but this remains unproven. Here, we used real and virtual experiments to test the hypothesis that cultivation selected for stronger competitive ability in wheats. First, we compared three independent domestication events across wheat species, showing that domesticated landraces were stronger competitors than their wild counterparts. Model simulations reproduced this finding, showing that competitiveness increased through larger, more erect leaves and greater apical dominance. A second experiment compared wild, landrace, and elite durum wheats, finding that stronger competitiveness arose early during domestication but has been reversed by modern breeding. Simulations showed that weaker competitiveness in modern varieties arose from smaller leaves and shorter internodes. Our work indicates that competition selected for domestication traits responsible for wheat canopy growth and architecture, resulting in competitive landrace phenotypes unsuitable for conventional modern agriculture.